class Dog: 
    """一次模拟小狗的简单尝试""" 
    def __init__(self, name, age): 
        """初始化属性 name 和 age""" 
        self.name = name 
        self.age = age 
    
    def sit(self):
        """模拟小狗收到命令时坐下""" 
        print(f"{self.name} is now sitting.") 
        
    def roll_over(self): 
        """模拟小狗收到命令时打滚""" 
        print(f"{self.name} rolled over!")


my_dog = Dog('Willie', 6)
print(f"My dog's name is {my_dog.name}.")
print(f"My dog is {my_dog.age} years old.")

my_dog.sit()
my_dog.roll_over()